1. Field of the Invention
The present invention relates to an ion implantation apparatus that is capable of implanting an ion beam extracted from an ion source into a wafer, and a control method thereof.
2. Description of Related Art
In general, an ion implantation apparatus has a configuration in which an ion source, an extraction electrode, a mass-analyzing magnet unit, a mass-analyzing slit, a beam scanner, a beam parallelizing device, an acceleration and deceleration device, an angular energy filter (AEF) device, a wafer processing chamber, a beam measuring device, and the like are disposed along a beam line. The ion implantation apparatus is used to implant ions into a wafer that is a semiconductor substrate using an ion beam extracted from the ion source.
Commonly, there are various beam measuring devices and methods suggested for measuring an amount of a beam current of the scanned ion beam that is parallelized after scanning a wafer in a reciprocation manner with the ion beam by a beam scanner, and a vertical (Y direction) profile and a horizontal (X direction) profile of the beam. The X direction and Y direction have the same meaning as an X-axis direction and a Y-axis direction, respectively.
There is disclosed a hybrid-type ion implantation apparatus in which a wafer is scanned with an ion beam in a reciprocating manner (may be called first scanning, beam scanning, or X-scanning) by a beam scanner with regard to an one-axis direction, for example, a horizontal direction, and the wafer is made to move in a reciprocating manner (may be called slow scanning or mechanical Y-scanning) by a mechanical Y-scanning device in a direction orthogonal to the one-axis direction, for example, in a vertical direction. In this ion implantation apparatus, as an example of a beam measurement and beam current control method, a method using measurement by a movable Faraday cup and beam scanning control by a beam deflection device is suggested (Japanese Patent No. 3153784). In the beam current control method using the beam measurement and the beam scanning control, a beam current of the scanned ion beam that is incident to the Faraday cup is measured while moving the Faraday cup along a scanning route of the scanned ion beam, and then the adjusted ion beam is measured at one side of an ion implantation position that is a wafer holding position at which ion implantation is performed. Here, the one side of the ion implantation position represents one side of two divided ion implantation regions, which are divided into two parts along the diameter of the wafer parallel in a Y-direction, in an ion implantation region of the wafer.
In the beam current control method using the beam measurement and the scanning control, before initiation of ion implantation, the beam current of the scanned ion beam that is incident to the Faraday cup is measured while moving the movable Faraday cup along the scanning route of the ion beam at an arbitrary position on a beam line, and then an amount of beam current of the adjusted ion beam is measured by a one-side beam current measuring instrument that is disposed at one side of the ion implantation position. The amount of the beam current is measured by only the one-side beam current measuring instrument. The movable Faraday cup does not perform measurement of a horizontal (X-direction) profile of the scanned ion beam (and a vertical (Y-direction) profile of the scanned ion beam).
In addition, in the above-described beam current control method, the scanned ion beam is measured by the movable Faraday cup and the one side beam current measuring instrument that is disposed in a stationary manner at the one side of the ion implantation position. However, in the above-described beam current control method, since the one side beam current measuring instrument is disposed in a stationary manner, it is impossible to perform beam measurement at a position on a side opposite to the one side of the ion implantation position, and beam measurement within a scanning range of the ion implantation position. Therefore, the beam current control using the beam measurement and the scanning control may be limited, and thus this limitation becomes a cause of obstruction to the request for measurement with high precision.
Therefore, as an example of the beam measurement method for improving the precision of the beam measurement and the beam current control, there is suggested a method in which in a beam scanning range between both scanning side positions in front of (upstream side) a wafer supporting platen that is the ion implantation position, and the rearmost position of the beam line behind the wafer supporting platen, the ion beam that is incident to this beam scanning range is measured by a Faraday cup disposed in a stationary manner (Japanese Patent No. 3257205).
The beam measurement method of Japanese Patent No. 3153784 has a configuration that a scanned ion beam is measured by a movable Faraday cup and a one-side beam current measuring instrument that is disposed in a stationary manner disposed at one side of the ion implantation position. However, in this beam measurement method, it is impossible to perform beam measurement at a position on a side opposite to the one side of the ion implantation position, and beam measurement within the scanning range of the ion implantation position. Therefore, the beam measurement may be limited, and thus this limitation becomes a cause of obstruction to the request for the high precision of the beam current control using the beam measurement and the scanning control.
On the other hand, the method disclosed in Japanese Patent No. 3257205 is a method of performing the beam measurement within the beam scanning range between both scanning side positions in front of the wafer supporting platen that is the ion implantation position, and the rearmost position of the beam line behind the wafer supporting platen. This method does not consider performing measurement of an ion beam, which is incident to the Faraday cup at an ion implantation position on the beam line and positions immediately in front of or behind the ion implantation position, by using the Faraday cup. Therefore, Japanese Patent No. 3257205 may not be applied to Japanese Patent No. 3153784.
In addition, in the method disclosed in Japanese Patent No. 3257205, measurement of a degree of uniformity of ion beam density in a horizontal direction, measurement of the total amount of the beam current, and measurement of the horizontal (X-direction) profile of the beam (and the vertical (Y-direction) profile of the beam) are reasonably set, and the adjustment of the ion beam is performed. Therefore, it is necessary for the method to be carried out to realize comprehensively optimized beam control.
In the hybrid-type ion implantation apparatus, a method of making a horizontal ion beam density distribution of the scanned ion beam in the first scanning direction (horizontal direction) uniform is disclosed, for example, in Japanese Patent No. 3153784. This method assumes a variation in a horizontal spot size of the beam to a certain amount, but does not assume expansion of the beam size such things as the beam remains on a target even at both ends of the beam scanning.
FIG. 10 illustrates an ion beam density distribution in a case where a beam size is small, and FIG. 11 illustrates an ion beam density distribution in a case where an ion beam is not swept away from the target at both ends of scanning when the beam size increases.
On the other hand, with regard to a beam tuning that is carried out before the uniformalizing of the horizontal ion beam density distribution of the scanned ion beam, when simple tuning is performed by only increasing a beam current value, the beam current may be increased, but the horizontal (X-direction) ion beam density distribution of the beam at the ion implantation position varies, and thus the beam size may be expanded.
In a case of an electrostatic beam scanner, the uniformalizing of the horizontal ion beam density distribution of the scanned ion beam is carried out by correcting (increasing or decreasing) a gradient dV/dt of an applied voltage of an alternating electric field (typically triangle wave) that is applied, but the correction does not operate well when the ion beam is not swept away from the target at both ends of scanning, and the horizontal ion beam density distribution of the scanned ion beam may not be uniformalized. This is because the beam current value at ends of the scanning range is determined by a factor other than original beam current intensity, and thus there is a contradiction to the correction itself of the gradient dV/dt of the applied voltage of the alternating electric field at that position.
To solve this problem, in the beam turning that is carried out before the uniformalizing of the scanned ion beam, it is necessary to tune both of the beam current value and the horizontal ion beam density distribution of a stationary beam at the same time by monitoring the horizontal distribution (horizontal stationary profile) of the stationary beam other than the beam current value.
To measure a horizontal (X-direction) stationary profile of the stationary beam, a Faraday cup having a thin slit that is long in the Y-direction is used, and it is necessary to perform the measurement by mechanically moving the Faraday cup in the X-direction. In a case of a hybrid-type ion implantation apparatus that performs electrostatic scanning by a beam scanner in the X-direction of the beam and mechanical Y-scanning in the Y-direction of the beam, for measurement of the horizontal stationary profile of the beam, it is necessary to obtain the horizontal stationary profile of the beam by moving the Faraday cup in the X-direction after stopping the electrostatic scanning of the beam, and by measuring stationary beam intensity distribution at each point in the X-direction.
However, in this method, a measurement time of one point is restricted by a mechanical movement time of the Faraday cup, and thus an increase in speed of the measurement is limited. Therefore, the method is not realistic for monitoring that is carried out for the tuning of the ion implantation apparatus in which an increase in speed is demanded.
In addition, with regard to parameter tuning, in a case where a response to be optimized is composed of a mono-variable, the parameter may be made to vary in order for the mono-variable to be a desired value. However, in a case where the response is composed of multi-variables, it is necessary to compose these variables and convert into one variable.
Consideration may be made for a hybrid-type ion implantation apparatus in which reciprocating scanning by the ion beam is performed by the beam scanner in one axis direction, for example, in the horizontal direction with an arbitrary first scanning frequency (beam scanning (first scanning) speed), and a wafer is made to move in a reciprocating manner by a mechanical Y-scanning device in a direction orthogonal to the one axis direction, for example, in the vertical direction with an arbitrary slow scanning frequency (a wafer scanning speed or a vertical scanning speed). In this hybrid-type ion implantation apparatus, in a case where a reciprocating scanning frequency of the beam is set to be variable, and the beam scanning speed of the reciprocating scanning is changed, particularly, in a case of using a slow beam scanning speed on a low frequency side, as shown in FIGS. 12A and 12B, when the first scanning frequency (beam scanning speed) closes to the slow scanning frequency (wafer scanning speed) and a beam size in the Y-direction decreases, a vertical beam overlapping width (overlapping amount) varies by the beam scanning of respective cycles, and thus the ion implantation distribution unevenness occurs in the vertical direction with respect to the wafer (target substrate). Therefore, the uniformity in a vertical ion implantation distribution deteriorates.
To solve this problem, in the beam turning that is carried out before the uniformalizing of the scanned ion beam, it is necessary to increase the Y-direction (vertical direction) beam size in order for the vertical ion implantation distribution to be uniform by monitoring the vertical ion beam stationary density (vertical profile) of the stationary beam according to X-direction (horizontal direction) and Y-direction (vertical direction) scanning frequencies other than the beam current value.